1. Field of the Invention
The present invention relates to a simplified method of designing a semiconductor integrated circuit, an apparatus for designing a semiconductor integrated circuit, a recording medium, and a mask manufacturing method.
2. Description of the Related Art
In recent years, the progress in techniques for manufacturing semiconductor devices is extremely remarkable. Semiconductor devices with sizes with a minimum machining dimension equal to or smaller than 0.1 μm are mass-produced. Such refining of semiconductor devices is realized by the rapid progress of fine pattern forming techniques and various EDA (Electronic Design Automation) tools for generating circuit patterns. In the ages when pattern sizes were sufficiently large, a plane shape of a large-scale integrated circuit (LSI) desired to be formed on a wafer was directly drawn as a design pattern, a mask pattern faithful to the design pattern was created, the mask pattern was transferred onto the wafer by a projection optical system, and a substrate was etched, whereby a pattern substantially the same as the design pattern could be formed on the wafer.
However, as refining of a pattern advances, it is becoming difficult to faithfully form patterns in the respective processes and final finish dimensions are not the same as those of the design pattern.
In particular, in lithography and etching processes most important to attain fine machining, other pattern layout environments arranged around a pattern desired to be formed significantly influence dimension accuracy of the pattern.
Therefore, in order to reduce the influence, there are optical proximity correction (OPC) and process proximity correction (PPC) techniques and the like (herein after referred to PPC methods) for adding an auxiliary pattern to a design pattern in advance to form dimensions after machining same as those of a desired pattern (see, for example, JP-A-9-319067).
On the other hand, a design flow for a layout performed upstream the mask data processing is timing-driven. In other words, a cell with an unreasonable drive force is used to fit operation speed of a transistor in a margin. Insertion of a buffer is frequently performed. A layout obtained as a result is subjected to timing verification. Under the present situation, such a design method has to be performed.
In the technique described above, as the optical proximity correction (OPC) and process proximity correction (PPC) techniques and the like become complicated, a pattern created by a designer and a mask pattern used during exposure are significantly different from each other. Therefore, it is difficult to easily predict a finish pattern shape on a wafer.
In layout design, the insertion of a buffer for converging timing resultantly causes an increase in a chip area. Moreover, usually, timing closure is performed in a transistor drawn in dimensions under worst conditions. Therefore, a load is applied to iteration for converging timing.
In this way, there are double loads of the layout design and the mask data processing (OPC and OPC verification processing) after design data is completed. Therefore, verification employing a process simulator is inevitably performed before shipment of a design pattern.
However, process verification for the design pattern is performed at a final stage of a design process. Therefore, feedback of a verification result moves design steps backward and a large load is applied to turn around time (TAT).
In order to solve the problem of TAT, there is proposed a method of data basing in advance design patterns that cause problems in OPC and coping with the problems with any one of design data, OPC, and lithography rule check (see, for example, JP-A-2006-126745). There is also proposed a method of quickly detecting and correcting, according to a vertex density, a pattern that causes a problem in OPC and a pattern that deteriorates a yield (see, for example, JP-A-2006-126745). There is also a proposal about a design method for arranging cells subjected to OPC in advance (see, for example, U.S. Pat. No. 6,425,117).
For example, in an arranging and wiring method of the method in the past, pre-filtering of a layout (extraction of a small margin pattern) is performed in arrangement of functional cells and schematic wiring of a semiconductor integrated circuit. The pre-filtering is filtering for applying process verification to the layout, mainly extracting a pattern that does not satisfy a process margin set in advance, i.e., causes the deterioration in a yield, and removing the pattern. Transfer simulation is applied to a mask pattern created by applying optical proximity correction (OPC) processing to the extracted pattern. When there is a problem as a result of the simulation, the pattern is corrected. Concerning the pattern that does not satisfy the process margin, process verification for a layout is performed at a full-chip level before the arrangement and the wiring are performed. A layout with a small process margin is categorized on the basis of a result of the process verification to create a database or a library. When process conditions, OPC, processing for OPC verification, and the like change, it is necessary to perform the verification again. Therefore, a large load is applied to preparation for the arrangement and wiring processing.
However, a problem not sufficiently coped with by the methods described above has occurred according to the refining and complication of patterns. In the method disclosed in JP-A-2006-126745, when a pattern is corrected at a stage of artwork, an increase in TAT is caused.
In the method disclosed in U.S. Pat. No. 6,425,117, a load is applied to OPC itself applied in advance. Moreover, in JP-A-2006-126745, accuracy of screening is not attained only with information on a vertex density of a pattern.
Moreover, in pattern matching and databasing for a reduction in TAT, as a result of process verification, there are too many variations of patterns that do not satisfy the process margin and a problem is caused. Therefore, it takes time to set up a library and a database. In future, it will be more difficult to put the pattern matching and databasing to practical use.
Furthermore, when refining of a pattern advances, it is likely that there are an enormous number of patterns that do not satisfy the process margin and categorization itself of the patterns fails.